Chromophores, sunscreen compositions and methods for preventing sunburn

ABSTRACT

The present invention relates to novel chromophore-containing compounds useful as sunscreen agents which have the ability to absorb both UVA and UVB wavelength radiation. These compounds comprise a specific type of UVA-absorbing chromophore covalently bonded to a specific type of UVB-absorbing chromophore. The chromophore moieties are covalently bonded together such that the electron systems of these moieties are directly coupled to thereby form a new chromophore. 
     The present invention further relates to sunscreen compositions containing the hereinbefore described type of sunscreen agents. Furthermore, the present invention relates to methods for protecting the skin of humans or lower animals from the effects of UVA and UVB wavelength radiation. This method comprises topically applying to the skin an effective coating of a sunscreen composition of the present invention.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 054,085, filed on Jun. 2,1987, which is a continuation-in-part of application Ser. No. 879,724filed Jun. 27, 1986.

BACKGROUND OF THE INVENTION

The present invention relates to novel chromophore compounds useful assunscreen agents. These chromophore compounds have the ability tostrongly absorb sunlight in both the UVA and UVB wavelength range. Thepresent invention further relates to novel skin protection compositionswhich are effective at protecting skin from both the UVA and UVBwavelength radiation component of sunlight. Finally, the presentinvention also relates to methods for protecting the skin from theeffects of UVA and UVB wavelength irradiation, such as sunburn andsun-induced aging of the skin.

The damaging effects of sunlight on skin are well documented. In spiteof this, people are forced to be in the sun for long periods of time dueto their occupations. Others are in the sun for long periods throughtheir leisure time activities and/or a desire to have a tannedappearance.

The major short term hazard of prolonged exposure to sunlight iserythema (i.e., sunburn). The 290 to 320 nanometer wavelengthultraviolet radiation range, which is designated by the cosmeticindustry as being the "UVB" wavelength range, is the most effective typeof UV radiation for producing erythema. The 320 to 400 nanometerwavelength ultraviolet radiation range, which is designated by thecosmetic industry as being the "UVA" wavelength range, also produceserythema.

In addition to the short term hazard of erythema caused by UVA and UVBsunlight, there are also long term hazards associated with this UVradiation exposure. One of these long term hazards is malignant changesin the skin surface. Numerous epidemologic studies have been conducted,and the results demonstrate a strong relationship between sunlightexposure and human skin cancer. Another long term hazard of ultravioletradiation is premature aging of the skin. This condition ischaracterized by wrinkling and yellowing of the skin, along with otherphysical changes such as cracking, telangiectasis (spider vessels),solar keratoses (growths), ecchymoses (subcutaneous hemmorrhagiclesions), and loss of elasticity. The adverse effects associated withexposure to UVA and UVB wavelength radiation are more fully discussed inDeSimone, "Sunscreen and Suntan Products", Handbook of NonprescriptionDrugs, 7th Ed, Chapter 26, pp. 499-511 (American PharmaceuticalAssociation, Washington, D.C.; 1982); Grove and Forbes, "A Method forEvaluating the Photoprotective Action of Sunscreen Agents Against UV-ARadiation", International Journal of Cosmetic Science, 4, pp. 15-24(1982); and U.S. Pat. No. 4,387,089, to DePolo, issued Jun. 7, 1983; thedisclosures of all of which are incorporated herein by reference. Hence,although the immediate effects of ultraviolet radiation may becosmetically and socially gratifying, the long-term effects arecumulative and potentially serious.

Sunscreen compositions comprising mixtures of molecules which absorb atdifferent UV wavelengths and which thereby protect the skin are known inthe art. For example, U.S. Pat. No. 4,264,581, to Kerkhof et al (issuedApr. 28, 1981), discloses a sunscreen composition containing a mixtureof 2-ethylhexyl dimethyl-para-amino benzoate and2-hydroxy-4-methoxy-benzophenone; U.S. Pat. No. 3,751,563, to Richardson(issued Aug. 7, 1973), discloses a sunscreen composition containing amixture of 2-ethoxyethyl para-methoxycinnamate, amyl para-dimethylaminobenzoate, homomenthyl salicylate, and 2-hydroxy-4-methoxybenzophenone;and U.S. Pat. No. 3,636,077, to Stauffer (issued Jan. 18, 1972),discloses sunscreen compositions containing salts of5-benzoyl-4-hydroxy-2-methoxy benzene sulfonic acid and 4-aminobenzoicacids or esters.

Notwithstanding the foregoing developments, there remains a continuingneed to identify new compounds and compositions which are effective forprotecting the skin from ultraviolet radiation in both the UVA and UVBradiation ranges. It is accordingly an object of the present inventionto provide new chromophore compounds which are effective sunscreeningagents for both UVA and UVB radiation, as well as sunscreen compositionscontaining these chromophore compounds. It is a further object of thepresent invention to provide methods for protecting the skin of humansor lower animals from the effects of exposure to UVA and UVB wavelengthradiation by employing sunscreening compounds and compositions of thepresent invention.

It is an additional object of the present invention to provide newchromophore compounds which have broad and strong absorption spectrathroughout both the UVA and UVB radiation range. It is a further objectof the present invention to provide sunscreening agents and compositionswhich are not readily absorbed by the skin; which have increasedsunscreen protection and decreased chance for allergy, irritation, ortoxicity problems resulting from use; and which are resistant to ruboff. A still further object is to provide sunscreen agents andcompositions which provide a constant and even protection against bothUVA and UVB radiation; which are cosmetically acceptable; and which arereadily formulated into sunscreen compositions.

These and other objects will become readily apparent from the detaileddescription which follows.

SUMMARY OF THE INVENTION

The present invention relates to novel chromophore-containing sunscreencompounds useful as sunscreen agents, which compounds are effective forabsorbing ultraviolet radiation in both the UVA and UVB wavelengthrange. These new compounds are formed by covalently linking a selectedUVA-absorbing chromophore moiety and a selected UVB-absorbingchromophore moiety together in the same molecule. These chromophoremoieties are linked such that the electron systems of the chromophoremoieties are directly coupled via this covalent linkage to thereby forma new chromophore-containing compound.

The present invention further relates to sunscreen compositions. Thesecompositions comprise a pharmaceutically-acceptable sunscreen carrierand a chromophore compound generally characterized by having both aUVA-absorbing chromophore moiety and a UVB-absorbing chromophore moiety.Again, the chromophore moieties are covalently linked such that theelectron systems of these moieties are directly coupled via the covalentlinkage.

Finally, the present invention also relates to methods for protectingthe skin of humans or lower animals from the effects of UVA and UVBwavelength radiation, such as sunburn and sun-induced aging of the skin.Such methods comprise topically applying to the human or lower animal aneffective coating of a sunscreen agent useful in the present invention.

DETAILED DESCRIPTION OF THE INVENTION Sunscreen Agents

The sunscreen agents useful in the present invention are novelchromophore-containing compounds which are derived from two chromophoremoieties that have different ultraviolet radiation absorption spectrums.In particular, one of the chromophore moieties absorbs predominantly inthe UVB radiation range, and the other absorbs strongly in the UVAradiation range. Further, these molecules have the chromophore moietieslinked in the molecule by covalent bonding, with this covalent linkagepermitting the electron systems of the chromophore moieties to bedirectly coupled through the linkage to thereby form a new chromophore.

More particularly, one of the chromophore moieties is characterized asbeing effective for strongly absorbing radiation in the UVA range whenthat chromophore moiety is isolated in an independent molecule. Theother chromophore moiety is characterized as being effective forabsorbing radiation predominantly within the UVB range when thatchromophore moiety is isolated in an independent molecule. These twochromophore moieties are covalently joined such that the electronsystems of these chromophore moieties are directly coupled, therebycreating the new chromophore-containing compounds of the presentinvention. Thus, the sunscreen agents useful in the present inventionare compounds having the general structure:

    X--B--Z.

In this general structure, the X group is a UVA-absorbing chromophorethat is a substituted, carbonyl-containing, aromatic ring-containingmoiety. This UVA-absorbing moiety when isolated as an independentchromophore would exhibit at least one absorption maximum (designatedherein as λmax, and described more fully hereinafter) within thewavelength range of from about 320 to about 400 nm. This absorptionmaximum would exhibit a molar absorptivity value (designated herein as"ε", and calculated as described hereinafter) of at least about 9,000,preferably at least about 20,000, and most preferably at least about30,000.

The Z group in the above general structure is a UVB-absorbingchromophore that is a substituted, carbonyl-containing, aromaticring-containing moiety. This UVB-absorbing moiety, when isolated as anindependent chromophore, would exhibit a molar absorptivity value of atleast about 4,000, preferably at least about 15,000, and most preferablyat least about 25,000, for at least one wavelength within the range offrom about 290 to about 320 nm. Preferably, when present as the solechromophore in a molecule as hereinafter defined, the Z group exhibitsat least one absorption maximum λmax within the range of from about 290to about 320 nm. This absorption maximum preferably has a molarabsorptivity value ε of at least about 4,000, more preferably at leastabout 15,000, and most preferably at least about 25,000. Finally, whenpresent as the sole chromophore in a molecule as hereinafter defined,the Z group furthermore should not exhibit a λmax having an ε greaterthan about 9,000 for any wavelength above about 320 nm.

Finally, in the above general structure the B group is a chemical bondor linking moiety which covalently bonds the two X and Z chromophoremoieties such that the electron systems of these chromophores aredirectly coupled, i.e., electrons are shared. Preferred is B selectedfrom a single bond, or atoms or groups of atoms which have freeelectrons which may be shared with both chromophore moieties, such as--O-- and --NR-- (wherein R is H, straight or branched chain alkylhaving from about 1 to about 20 carbon atoms, (CH₂ CH₂ O)_(m) --H, or(CH₂ CH(CH₃)O)_(m) --H, wherein m is an integer from 1 to about 8, andpreferably m=1 to about 3). Most preferred is B being --NH-- and,especially, --O--.

The sunscreen agents of the present invention preferably absorb light inthe visible wavelength range (i.e., above about 400 nm) only weakly ornot at all. The compounds are therefore either only lightly colored(e.g., light yellow or cream colored) or are essentially white. This isdesirable for cosmetic reasons. Thus, the sunscreen agents preferably donot have an ε of greater than about 500 for any wavelength above about400 nm, and most preferably the ε is essentially zero for any wavelengthabove about 400 nm.

It is further preferred that the compounds of the present invention belower molecular weight compounds, preferably having a molecular weightof less than about 2,500, and most preferably less than about 1,000.Furthermore, the compounds are preferably liquids above about 10° C.

Specifically, examples of suitable X chromophore moieties useful in thesunscreen compounds of the present invention include ##STR1## In all thepreceding formulae, each A is a substituent independently selected fromthe group consisting of R, --OR, --NR₂, or --SO₃ H, or itspharmaceutically-acceptable salt or ester; each A² is independently --ORor --NR₂ ; each A³ is independently H or OH; each A⁴ and A⁵ are,independently, R or OR, and wherein further either A³ or A⁴ must be OH;each A⁶ is independently H or --SO₃ H, or itspharmaceutically-acceptable salt or ester; and each R is independentlyH, straight or branched chain alkyl having from about 1 to about 20carbon atoms, (CH₂ CH₂ O)_(m) --H, or (CH₂ CH(CH₃)O)_(m) --H, wherein mis an integer from 1 to about 8, and preferably m=1 to about 3.

Preferred as the X chromophore moiety are the groups ##STR2##Preferably, either A³ or A⁴ is OH, with the other group being H; A⁵ isR; and A⁶ is H. Most preferably, A³ is OH, and A⁴, A⁵ and A⁶, are H. Ais preferably R, and most preferably A is H.

Also specific examples of the Z chromophore moieties useful in thesunscreen compounds of the present invention include: ##STR3##

In these preceding formulae, each A¹ is independently --CN or --CO₂ R¹ ;each A⁷ is independently --OR or --O₂ C--R¹, except that both A⁷ and A³(described hereinbefore for the X groups) are not --OH; each R¹ isindependently straight or branched chain alkyl having from about 1 toabout 20 carbon atoms; and the A² and R substituent groups are asdescribed hereinbefore for the substituted X groups.

Preferred as the Z chromophore moiety are the groups ##STR4##Preferably, --NR₂ is --NR¹ ₂. Both R¹ groups may be different alkylgroups. Particularly preferred is one R¹ group having more than about 2carbon atoms (especially branched-chain alkyl groups, e.g.,2-ethyl-hexyl), the other R¹ group being methyl or ethyl, especiallymethyl. Alternatively, both R¹ groups are the same alkyl group,preferably 2-ethylhexyl. Also preferred is A² being --OR or --NR₂(preferably the --NR₂ is --NR¹ ₂ as described hereinbefore). Mostpreferred A² is --OCH₃, --OCH₂ CH₃, OH, or --NR² ₂ (wherein one R¹ grouphas more than about 2 carbon atoms, especially branched-chain alkyl, andthe other R¹ group is methyl or ethyl, especially methyl).

Preferred sunscreen agents of the present invention have the generalstructures: ##STR5##

Especially preferred are the last two structures, with the laststructure being most preferred. The B group and substituents on thesestructures are preferably as described hereinbefore.

Specific sunscreen agents of the present invention include, for example:##STR6## 4-N,N-dimethylaminobenzoic acid ester with4-hydroxydibenzoylmethane ("Compound 1"); ##STR7## 4-methoxycinnamicacid ester with 4-hydroxydibenzoylmethane ("Compound 2");4-methoxycinnamic acid ester with 4-hydroxy-4'-methoxydibenzoylmethane("Compound 3"); ##STR8## 4-N,N-(2-ethylhexyl)methylaminobenzoic acidester with 4-hydroxydibenzoylmethane ("Compound 4"); and ##STR9##4-N,N-dimethylaminobenzoic acid ester with 2,4-dihydroxybenzophenone("Compound 5"); ##STR10## N,N-di(2-ethylhexyl)-4-aminobenzoic acid esterwith 4-hydroxydibenzoylmethane ("Compound 6"); and ##STR11##4-N,N-(2-ethylhexyl) methylaminobenzoic acid ester with2,4-dihydroxybenzophenone ("Compound 7").

The sunscreen agents of the present invention can be prepared fromcommercially-available, chromophore-containing molecules. Typically, thesynthesis of the sunscreen agents will be achieved by an esterificationor amidation reaction. Synthesis techniques which are generallyapplicable for synthesizing sunscreen agents of the present inventionare taught, for example, in U.S. Pat. No. 4,002,733, issued Jan. 11,1977, to Degen et al.; and in U.S. Pat. No. 4,115,547, issued Sep. 19,1978, to Degen et al.; the disclosures of both these patents beingincorporated herein by reference. Representative procedures forsynthesizing the sunscreen agents of the present invention are providedin the Examples hereinafter.

The term "pharmaceutically-acceptable salts and esters", as used herein,means those ester and salt forms of the sunscreen agents which areacceptable from a toxicity viewpoint. Pharmaceutically-acceptable saltsinclude alkali metal (e.g., sodium and potassium), alkaline earth metal(e.g., calcium and magnesium), non-toxic heavy metal (e.g., stannous andindium), and ammonium and low molecular weight substituted ammonium(e.g., mono-, di-, tri- and tetra-substituted amine which aresubstituted with methyl and/or ethyl) salts. Preferred are the sodium,potassium, and ammonium salts. Pharmaceutically acceptable estersinclude straight or branched chain alkyl ester having from 1 to about 20carbon atoms, preferably the methyl or ethyl ester.

The term "independent chromophore", as used herein, means thechromophore moiety (i.e., either the X or Z group) when it is bonded to--O--R² (wherein R² represents a short chain alkyl group, e.g., methylor ethyl; preferably methyl) rather than the chromophore moiety beingbonded to the B linking moiety within the X--B--Z compound. For example,independent chromophores of Compound 5 described hereinbefore are theethyl ester of 4-N,N-dimethylaminobenzoic acid and2-hydroxy-4-methoxybenzophenone. Also as an example, independentchromophores of Compound 4 described hereinbefore are the methyl esterof 4-N,N-(2-ethylhexyl)methylaminobenzoic acid and4-methoxy-dibenzoylmethane.

The term "molar absorptivity value", as used herein, is a quantitativemeasure of the ability of a molecule to absorb ultraviolet light at aspecified wavelength. The molar absorptivity value is expressed at aparticular wavelenght of light as the molar absorption coefficient(represented herein by "ε" which is expressed in units of liter/molecm), which is calculated by the equation: ##EQU1## wherein "l" is thepath length (in centimeters) of the absorbing media through which thelight passes; "c" is the concentration of the chromophore molecule (inmoles per liter); and "A" is the "absorbance". The absorbance iscalculated from the observed difference in the intensity of theparticular wavelength of light before and after passing through thechromophore-molecule-containing absorbing media. Thus, the absorbance iscalculated by the equation: ##EQU2## wherein "I₀ " is the intensity of aparticular wavelength of incident radiation on an absorbing path; and"l" is the intensity of the same particular wavelength of transmittedradiation which has passed through the absorbing path.

The calculation of the molar absorptivity value for a particularwavelength of light is well-known in the art, and is taught in moredetail in Atlas of Spectral Data and Physical Constants for OrganicCompounds, 2nd Ed., Vol. I, pp. 399-408 (Grasselli and Ritchey, Editors;CRC Press, Inc., Cleveland, Ohio, 1975), the disclosures of which areincorporated herein by reference. Instruments useful for making theintensity measurements for the calculation of the molar absorptivityvalue are also well-known in the art (e.g., Varion DMS-100 and BeckmanDU-7). Molar absorptivity values for representative compounds of thepresent invention are provided in the Examples hereinafter.

The term "absorption maximum", as used herein, means a wavelength ofradiation at which the chromophore-containing molecule has the greatestmolar absorptivity value relative to wavelengths immediately above andbelow the absorption maximum wavelength. Thus, in the typical spectrumof UV-radiation absorption, the absorption maximum are easily identifiedas peaks in the graph of the spectrum generated by the instrumentmeasuring the UV absorption. Absorption maximum (designated herein asλmax) are provided for representative sunscreen compounds of the presentinvention in the Examples hereinafter.

The sunscreen agents useful in the present invention have severaldesirable properties relative to a simple mixture of a UVA-absorbingmolecule with a UVB-absorbing molecule. Particularly beneficial is thelarge values and broad absorption spectra of the novel chromophores ofthe present invention. This permits the use of lower amounts ofsunscreen agent of the present invention, relative to a mixture ofmolecules, to achieve the same quantity of sunscreen protection.Furthermore, this translates into better sunscreen protection throughoutthe entire UVA and UVB radiation range.

An additional benefit from the present invention is the certainty ofproviding both UVA and UVB protection at the same site on the skin. Amixture of molecules may lack this uniformity due to non-uniformdistribution onto the skin surface and/or selective penetration by onetype of molecule through the skin versus the other type of molecule. Arelated benefit is that the sunscreen agents of the present inventionprovide a constant relative proportion of UVA to UVB protection. Amixture of chromophore molecules may not maintain a constant relativeproportion of UVA to UVB protection because one chromophore may be morereadily lost from the skin (e.g., by a higher rate of rub-off or skinpenetration) than the other chromophore. Another benefit is that thesunscreen agents of the present invention are absorbed more slowly bythe skin than mixtures of the independent chromophores. This translatesinto longer duration of protection for the skin, and less potential forskin irritation resulting from absorption by the skin. The ability ofthe sunscreen compounds of the present invention, and of mixtures ofindependent chromophores, to absorb UV radiation may be measured by invitro methods known generally in the art, such as those taught in Sayreet al., "A Comparison of in vivo and in vitro Testing of SunscreeningFormulas", Photochem. Photobiol., 29, 559-566 (1979), the disclosures ofwhich are incorporated herein by reference. Some of the compounds of thepresent invention may also be more resistant to wash-off by water fromsweat or swimming.

The sunscreen agents of the present invention typically comprise fromabout 0.1% to about 99.9% by weight of the sunscreen compositions of thepresent invention, preferably from about 1% to about 20%, and mostpreferably from about 5% to about 15%.

Pharmaceutically-Acceptable Sunscreen Carriers

In addition to a sunscreen agent as described hereinbefore, thesunscreen compositions of the present invention essentially contain apharmaceutically-acceptable sunscreen carrier. The term"pharmaceutically-acceptable sunscreen carrier", as used herein, meansone or more substantially non-irritating compatible filler diluentswhich are suitable for topical application to the skin of a human orlower animal. The term "compatible", as used herein, means that thecomponents of the carrier must be capable of being comingled with thesunscreen agent, and with each other, in a manner such that there is nointeraction which would substantially reduce the efficacy of thecomposition during use for protecting the skin from the effects of UVAand UVB wavelength radiation. Pharmaceutically-acceptable sunscreencarriers must, of course, be of sufficiently high purity andsufficiently low toxicity to render them suitable for topicaladministration to the human or lower animal.

The sunscreen compositions of the present invention containpharmaceutically-acceptable sunscreen carriers selected as appropriatefor the formulation desired. For example, it is possible to preparesunscreen compositions of the present invention in the form of organicsolvent solutions, aqueous emulsions, gels, or aerosol formulation.Preferred are sunscreen compositions of the present invention formulatedas aqueous emulsions. The pharmaceutically-acceptable sunscreen carriersuseful in the compositions of the present invention include, forexample, water, oils, fats, waxes, synthetic polymers, emulsifiers,surfactants, perfumes, dyes, preservatives, artificial tanning agents(e.g., dihydroxyacetone), and conventional sunscreening agents (e.g.,octyl N,N-dimethyl-para-aminobenzoate; 2-hydroxy-4-methoxybenzophenone).

Water is typically the major component of the sunscreen compositions ofthe present invention. Generally, water is present at a level of fromabout 50% to about 99% by weight of the composition, preferably fromabout 70% to about 96%, and most preferably from about 75% to about 85%.

Emulsifiers are preferably included in the sunscreen compositions of thepresent invention, preferably comprising from about 1.5% to about 10% byweight of the composition, and most preferably from about 2% to about5%. Preferred emulsifiers are anionic or nonionic although other typesmay also be used. Suitable emulsifiers are disclosed in, for example,U.S. Pat. No. 3,755,560, issued Aug. 28, 1973, to Dickert et al.; U.S.Pat. No. 4,421,769, issued Dec. 20, 1983, to Dixon et al.; andMcCutcheon's Detergents and Emulsifiers, North American Edition, 1983;with the disclosures of these references being incorporated herein byreference.

Types of emulsifiers useful in the sunscreen compositions of the presentinvention include ethoxylated fatty acids, ethoxylated esters,ethoxylated ethers, ethoxylated alcohols, phosphated esters,polyoxyethylene fatty ether phosphates, fatty acid amides, acyllactylates, soaps and mixtures thereof. Fatty alcohols such as cetyl andstearyl alcohol, and cetearyl alcohol are also regarded as emulsifiersfor purposes of the present invention.

Examples of such emulsifiers include polyoxyethylene (8) stearate,myristyl ethoxy (3) myristate, polyoxyethylene (100) monostearate,lauric diethanolamide, stearic monoethanolamide, hydrogenated vegetableglycerides, sodium steroyl-2-lactylate and calcium stearoyl-2-lactylate.Soaps are also acceptable emulsifiers. The soaps may be formulated insitu in processing the compositions and are preferably alkali metal ortriethanolamine salts of long-chain fatty acids. Such soaps includesodium stearate, triethanolamine stearate and the similar salts oflanolin fatty acids.

Also preferred for use in the compositions of the present invention is acopolymer of ethylene and acrylic acid. These monomers:

    ______________________________________                                        Ethylene:           CH.sub.2CH.sub.2                                          Acrylic Acid:                                                                                      ##STR12##                                                ______________________________________                                    

are present in polymeric form as follows: ##STR13## wherein the ratio ofx:y is from about 1:24 to about 1:9. The weight average molecular weightis from about 3,500 to about 4,500, preferably from about 4,000 to about4,300.

The compositions of the present invention may also contain in additionto the aforementioned components, a wide variety of additional oilsoluble materials and/or water soluble materials.

Among the oil soluble materials are non-volatile silicone fluids such aspolydimethyl siloxanes with viscosities ranging from about 10 to about100,000 centistokes at 25° C. These siloxanes are available from DowCorning Corporation as the Dow Corning 200 series.

Other oil soluble materials include fatty acid alcohols such as cetylalcohol and stearyl alcohol; esters such as cetearyl palmitate, laurylmyristate and isopropyl palmitate; oils such as castor oil, jojoba oil,cottonseed oil, peanut oil and sesame oil; waxes such as petrolatum,ceresin wax, carnauba wax, beeswax, and castor wax; lanolin, itsderivatives and components such as acetylated lanolin, lanolin alcoholsand lanolin fatty acids. Sterols such as cholesterol and phytosterol arealso useful herein.

These optional oil phase materials may individually comprise up to about20% by weight of the total sunscreen composition, preferably up to about10%.

Additional water soluble materials may also be present in thecompositions of this invention. Included are humectants such asglycerine, sorbitol, propylene glycol, alkoxylated glucose andhexanetriol; tyrosine; thickening agents such as carboxyvinyl polymers(Carbopols®-- offered by B. F. Goodrich Company, such polymers aredescribed in detail in U.S. Pat. No. 2,798,053, issued Jul. 2, 1957 toBrown, incorporated herein by reference); ethyl cellulose, polyvinylalcohol, carboxymethyl cellulose, vegetable gums and clays such asVeegum® (magnesium aluminum silicate, R. T. Vanderbilt, Inc.); proteinsand polypeptides; preservatives such as the methyl, ethyl, propyl andbutyl esters of hydroxybenzoic acid (Parabens--Mallinckrodt ChemicalCorp.), EDTA, methylisothiazolinone and imidazolidinyl ureas (Germall115--Sutton Laboratories); and an alkaline agent such as sodiumhydroxide or potassium hydroxide to neutralize, if desired, part of thefatty acids or thickeners which may be present.

The water phase materials may individually comprise up to about 20% byweight of the total sunscreen composition, preferably up to about 10%.

The present compositions may also contain agents suitable for aestheticpurposes such as perfumes and/or dyes.

The pH of the sunscreen compositions herein is preferably in the rangeof from about 4.5 to about 9.

For an aqueous emulsion sunscreen composition of the present invention,the mean particle size of the dispersed oil phase materials (e.g.,sunscreen agent, polymer, perfumes, etc.) dispersed in the aqueous phasemay be in the range of from about 5 to about 10 microns with greaterthan about 75% of the particles being less than about 12 microns.

The pharmaceutically-acceptable sunscreen carriers, in total, typicallycomprise from about 0.1% to about 99.9% by weight of the sunscreencompositions of the present invention, preferably from about 80% toabout 99%, and most preferably from about 85% to about 95%.

The compositions of the present invention may be prepared using themethod described in the examples hereinafter.

Method for Preventing Sunburn

The present invention further relates to a method for protecting theskin of humans or lower animals from the effects of UVA and UVBwavelength radiation, such as sunburn and premature aging of the skin.Such a method comprises topically applying to the human or lower animalan effective coating of a sunscreen agent of the present invention, or,preferably, of a sunscreen composition of the present invention. Theterm "effective coating", as used herein, means a film of sunscreenagent sufficient to substantially reduce the amount of UVA and UVBwavelength light which reaches the skin's surface. Typically, aneffective coating of the skin is from about 0.5 mg sunscreen agent ofthe present invention/cm² skin to about 5 mg sunscreen agent of thepresent invention/cm² skin.

The following examples further describe and demonstrate the preferredembodiments within the scope of the present invention. The examples aregiven solely for the purpose of illustration, and are not to beconstrued as limitations of the present invention since many variationsthereof are possible without departing from its spirit and scope.

EXAMPLE 1 Synthesis of Compound 4

(a) Synthesis of 4-N,N-(2-ethylhexyl)methylaminobenzoic acid

A 1000 mL, 3 necked, round-bottomed flask equipped with an overheadstirrer, dropping funnel, and reflux condenser is charged with4-N-methylaminobenzoic acid (25.0 g, 0.165 mol Aldrich Chemical Co.,Milwaukee, Wis.), 130 mL of toluene, glacial acetic acid (40.0 g), andzinc dust (42.5 g, 0.65 g atom). This mixture is heated to reflux withstirring at which time a dropwise addition of 2-ethylhexanol (84.6 g,0.66 mol) is begun. After the addition is completed, the reactionmixture is refluxed for 16 hours. TLC analysis (silica gel, 50/50hexane/acetone) shows that not all of the acid is reacted. An additional7.0 g of zinc dust and 2 mL of glacial acetic acid is added. After 2hours of additional reflux, TLC analysis shows the starting acid to beconsumed. The hot solution is filtered through a Celite.sup.(R) filtercake on a medium sintered glass funnel and washed with 100 mL of hottoluene. The filtrate is poured into a separatory funnel containing 200mL of water and 500 mL of chloroform. The mixture is brought to pHapproximately 1 with concentrated hydrochloric acid. After shakingintimately, the chloroform layer is drained off and the aqueous layer isextracted with chloroform (3×150 mL). The combined chloroform extractsare washed with 150 mL of brine and dried over magnesium sulfate. Afterfiltration and removal of the solvents by rotary evaporation (0.1 Torr,100° C. water bath), 40.4 g of a light brown waxy solid is obtained.This material is recrystallized from 120 mL of 90% ethanol to yield 30.2g of a fluffy white solid, m.p. 55.5°-57.5° C. Anal. calcd. for C₁₆ H₂₅O₂ N: C, 72.96; H, 9.57; O, 12.15; N, 5.32. Found: C, 73.11; H, 9.62; O,12.28; N, 5.23.

Alternatively, N-(2-ethylhexyl)-N-methyl-4-aminobenzoic acid can beprepared by the following method. Ethyl 4-aminobenzoate is dissolved in1;1 acetic acid/ethanol with 2-ethyl hexanal. Then 10% Pd on Carbon (2kg benzoate/75 g catalyst) is added. This mixture is placed underhydrogen at room temperature for one hour. The reaction is thendetermined to be complete by TLC. An excess of 40% aqueous formaldehydeis added and the reaction again placed under hydrogen at 30°-35° C. forone hour. The reaction is complete by TLC. The reaction mixture is thenfiltered through Celite and the solvents removed. The resulting materialis partitioned between water and methylene chloride. The methylenechloride layer is then washed with saturated sodium bicarbonate. Theresulting methylene chloride layer is then dried over magnesium sulfateand the volatiles are removed after filtration to give the desiredproduct as the ethyl ester. This material is placed in 12 volumes ofethanol/water (65:35) per weight of ethyl ester. Two mole equivalents ofsodium hydroxide are added and the mixture refluxed for two hours. Thereaction is then complete by TLC. Most of the ethanol is removed andmore water added followed by the hydrochloric acid. The resultingdesired carboxylic acid then precipitates. The total process is close toquantitative. Recrystallization of the product is in 2 kg acid per 4.5liters of ethanol. About a 70% recovery of material is observed.

(b) Synthesis of 4-hydroxydibenzoylmethane

A 1000 mL, 3 necked, round-bottomed flask equipped with an overheadstirrer, dropping funnel, and reflux condenser is charged with sodiumhydride 80% oil dispersion (12.0 g, 0.40 mol) which is washed twice withhexane. Next, 200 mL of freshly distilled glyme is added and the slurryheated to reflux with stirring. A solution of 4-hydroxyacetophenone(13.62 g, 0.10 mol) dissolved in 100 mL of glyme is added dropwise. Thereaction mixture is allowed to reflux for 45 minutes after the addition.Next, a solution of methyl benzoate (13.62 g, 0.10 mol) dissolved in 100mL of glyme is added dropwise. The reaction mixture is allowed to refluxfor 16 hours, after which time most of the glyme was distilled off ataspirator pressure. The pot residue is cooled in an ice bath and 300 mLof ether is added followed by the cautious addition of 200 mL of water.The mixture is poured into a separatory funnel, shaken intimately, andthe aqueous layer removed. The ether layer is washed with cold water(2×200 mL) followed by 100 mL of cold 1% aqueous NaOH. The combinedaqueous layers are carefully poured onto a mixture of 400 g of ice plus90 mL of concentrated HCl. The yellowish green solid that precipitatesis collected by suction filtration and washed with a little cold water.This material is recrystallized from 95% ethanol to yield 13.1 g of ayellow solid, m.p. 153°-156° C. Anal. calcd. for C₁₅ H₁₂ O₃ : C, 74.99;H, 5.03; O, 19.98. Found: C, 74.72; H, 5.02; O, 19.80.

(c) Synthesis of Compound 4

A 50 mL, round-bottomed flask equipped with a magnetic stir bar ischarged with 4-N,N-(2-ethylhexyl)methylaminobenzoic acid (1.22 g, 4.62mmol), 4-hydroxydibenzoylmethane (1.11 g, 4.62 mmol), and 10 mL DMF. Tothe golden solution is added 9.2 mL of polyphosphate ester and anadditional 10 mL of DMF. The reaction mixture is heated to 85° C. for 40hours. The deep red reaction mixture is poured into 25 mL of cold waterto yield a yellow precipitate which is collected by suction filtrationand washed with a little water. This material is recrystallized fromethanol to give 1.45 g of a light yellow solid, m.p. 90°-91.5° C. Analcalcd for C₃₁ H₃₅ O₄ N: C, 76.68; H, 7.26; O, 13.18; N, 2.88. Found: C,76.13; H, 7.50; O, 13.59; N, 2.84.

The UV spectrum of Compound 4 (isopropanol solution) exhibits a λmax=338nm (ε=51,350).

EXAMPLE 2 Synthesis of Compound 5

By a procedure analogous to that described hereinbefore in Example 1,Compound 5 is synthesized from 4-N,N-dimethylaminobenzoic acid and2,4-dihydroxybenzophenone (both from Aldrich Chemical Company;Milwaukee, Wis.). The UV spectrum of Compound 5 (isopropanol solution)exhibits a λmax=321.5 (ε=42,490).

EXAMPLE 3 Synthesis of Compound 1

By a procedure analogous to that described hereinbefore in Example 1,Compound 1 is synthesized from 4-N,N-dimethylaminobenzoic acid (AldrichChemical Company; Milwaukee, Wis.) and 4-hydroxydibenzoylmethane (whichis prepared as described in Example 1b). mp=195°-197° C. The UV spectrumof Compound 1 (isopropanol solution) exhibits a λmax=336 (ε=44,920).

EXAMPLE 4 Synthesis of Compound 2 (a) Synthesis of 4-methoxycinnamoylchloride

A 1000 mL round bottom flask equipped with a magnetic stir bar, refluxcondenser, dropping funnel, and argon inlet is charged with 30.0 g (0.17mol) of 4-methoxycinnamic acid and 500 ml of benzene. Next, 40.5 ml(66.1 g, 0.56 mol) of thionyl chloride is added dropwise. After theaddition is complete, the reaction mixture is heated to reflux for fivehours. Heating is discontinued and the mixture allowed to stirovernight. The benzene is removed by rotary evaporation to yield 33.6 g(0.17 mol, 100%) of a beige solid. Proton NMR and IR are consistent withthe proposed structure. This material is used without furtherpurification.

(b) Synthesis of Compound 2

A 50 mL, round-bottomed flask equipped with a magnetic stir bar and areflux condenser is charged with 4-methoxycinnamoyl chloride (1.0 g, 5.0mmol) and 25 mL freshly distilled THF. This mixture then is chilled inan ice salt bath. Next, a solution of 4-hydroxydibenzoylmethane (1.0 g,4.0 mmol; which is prepared as described in Example 1b) dissolved in amixture of 3 mL dry pyridine and 5 mL THF is added dropwise to thereaction flask. The reaction mixture is then heated to reflux for 1hour, after which time the reaction mixture is cooled and poured into amixture of 20 g of ice and 3 mL conc. hydrochloric acid. The fine whitesolid which precipitates is collected by suction filtration;m.p.=149°-151° C. Analysis calcd. for C₂₅ H₂₀ O₅ : C, 74.99; H, 5.03; O,19.98. Found: C, 74.77; H; 5.03; O, 20.12. The UV spectrum of Compound 2(isopropanol solution) exhibits a λmax=338 (ε=47,200).

EXAMPLE 5 Synthesis of Compound 3 (a) Synthesis of4-hydroxy-4'-methoxydibenzoylmethane

This compound is prepared by a procedure analogous to the procedure usedto prepare 4-hydroxydibenzoylmethane, but using methyl 4-methoxybenzoatein place of the methyl benzoate as used in Example 1b. mp=180°-182° C.Anal. calcd for C₁₆ H₁₄ O₄ : C, 71.10; H, 5.22; O, 23.68. Found: C,71.15; H 5.54; O, 23.47.

(b) Synthesis of Compound 3

By a procedure essentially the same as that described in Example 4hereinbefore, Compound 3 is synthesized from 4-methoxycinnamoyl chloride(which is prepared as described in Example 4a) and4-hydroxy-4'-methoxydibenzoylmethane. The crude material isrecrystallized from acetone to yield a light yellow solid;mp=147.5°-149° C. The UV spectrum of Compound 3 (isopropanol solution)exhibits a λmax=351 (ε=45,000).

EXAMPLE 6 Synthesis of Compound 6

A 100 mL, round-bottomed flask equipped with a magnetic stir bar, acondenser and positive nitrogen is charged withN,N-di-(2-ethylhexyl)-4-aminobenzoic acid (5.0 g, 0.0138 mole, F. W.361). To this is added 4-hydroxydi-benzoylmethane (3.32 g, 0.0138 mole,F. W. 240), followed by 30 mL of polyphosphate reagent (made byrefluxing a mixture of, for example, 161 g (1.14 mole) of phosphoruspentoxide, 151 mL anhydrous ether and 322 mL of chloroform for 16hours). This solution is stirred magnetically and heated in an oil-bathfor 16 hours, at 80° C.

This reaction mixture is then allowed to cool and 100 mL of anhydrousdiethyl ether is added. The resulting two phases are separated. Theether layer is washed with 50 mL of saturated sodium bicarbonate anddried over anhydrous magensium sulfate. This mixture is then filteredand roto-evaporated to yield 5.64 g of an orange oil. (Theory yield oftitle compound 8.04 g). TLC (70/30 hexane/acetone) indicates mostlyproduct r.f. 0.75.

This material is further purified by the HPLC to give material which ispure by TLC and the H-NMR, C-13 NMR, IR and Mass Spectra are inagreement with this structure and purity. H-NMR; DCCl₃ /TMS: 0.6-2.0(m),3.3(d), 6.5-6.8(m), 7.1-7.6(m), 7.8-82(m). C-13 NMR; DCCl₃ /TMS: 185.26,164.88, 154.92, 152.21, 135.45, 132.40, 132.05, 128.66, 127.10, 122.21,114.26, 93.01, 56.21, 36.86, 30.58, 28.68, 23.90, 23.15, 14.06, 10.71,IR salt plates: 2957m, 2912m, 2863m, 1715m, 1600s, 1520w, 1460w, 1271m,1210m, 1180s, 1163s, 1060m, 1050m, 1015s, 1007s, 735s, 650m. Massspectrum parent ion=583.

The UV spectrum of Compound 6 (ClCH₂ CH₂ Cl solution) exhibits aλmax=342.1 nm (ε=31,000).

EXAMPLE 7 Synthesis of Compound 7

The following reagents are placed into a 50 ml flask equipped with amagnetic stirrer and a drying tube:N-(2-ethylhexyl)-N-methyl-4-aminobenzoate and 5.0 ml of polyphosphateester (prepared by refluxing 204 g of phosphorous pentaoxide, 200 mlanhydrous diethyl ether and 425 ml of chloroform for 16 hours whichresults in a homogeneous solution). This mixture is then heated for 4hours at 80° C. The homogeneous reaction solution is then allowed tocool and TLC (methylene chloride/methanol 99/1 on silica gel G)indicates most of the starting materials are gone and two new spots atlarger r.f. values are present. This reaction solution is poured into 50ml of methylene chloride and washed with 25 ml saturated sodiumbicarbonate and 10 ml water. The resulting methylene chloride layer isthen dried over magnesium sulfate. The mixture is filtered and thevolatiles are removed by rotoevaporation to give 1.2 of oil. The oil isthen purified by HPLC to give two isomers. Mass spectral and NMR dataconfirm the structure of these compounds.

The UV spectrum of Compound 7 exhibits a λmax=331.1 nm (ε=26,480).

EXAMPLES 8-14

The following sunscreen compositions are representative of the presentinvention:

    __________________________________________________________________________              Example #                                                                     Weight %                                                            Component:                                                                              8    9    10   11   12   13   14                                    __________________________________________________________________________    Sunscreen                                                                     Compound:                                                                     #(1)      10   --   --   --   --   7.5  --                                    #(2)      --   3    --   --   --   --   --                                    #(3)      --   --   6    --   --   --   4.9                                   #(4)      --   --   --   10   --   --   2.1                                   #(5)      --   --   --   --   7.5  10   --                                    Ethylene/Acrylate                                                                       0.75 0.25 0.45 0.75 0.75 1.25 0.5                                   Copolymer.sup.1                                                               Glycerin  3.50 6.00 5.50 4.00 3.50 2.00 5.0                                   Petrolatum                                                                              1.50 2.50 2.00 --   1.50 0.50 2.0                                   Dimethicone.sup.2                                                                       0.30 0.50 0.30 0.40 0.30 0.20 0.40                                  Steareth-100                                                                            0.48 0.48 0.7  0.3   0.375                                                                             0.90 0.70                                  Glycerol  0.32 0.32 0.8  0.7   0.875                                                                             0.80 0.30                                  Monostearate                                                                  Cetyl Alcohol                                                                           1.20 1.2  1.0  1.0  1.0  1.50 1.20                                  Stearic Acid                                                                            0.52 0.52 0.52 0.52 0.52 0.52 0.52                                  Carbopol 934.sup.3                                                                      0.08 0.08 0.15 0.09 0.18 0.20 0.10                                  Carbopol 941.sup.3                                                                      0.06 0.06 0.08 0.09 0.05 0.05 0.10                                  Methyl Paraben.sup.4                                                                    0.20 0.2  0.2  0.2  0.20 0.2  0.20                                  Propyl Paraben                                                                          0.10 0.1  0.1  0.1  0.10 0.1  0.10                                  Imidazolidinyl                                                                          0.10 0.1  0.1  0.1  0.10 0.1  0.10                                  Urea                                                                          Tetrasodium                                                                             0.10 0.1  0.1  0.1  0.10 0.1  0.10                                  EDTA                                                                          Tyrosine  0.10 0.1  0.1  0.1  0.10 0.1  0.10                                  Potassium 0.31 0.35 0.37 0.31  0.395                                                                             0.32 0.37                                  Hydroxide                                                                     Titanium Dioxide                                                                        0.30 0.20 0.30 0.40 0.40 0.50 0.40                                  Perfume   0.18 0.08 0.15 0.13 0.10 0.25 0.15                                  Water     79.90                                                                              83.86                                                                              81.08                                                                              80.71                                                                              79.455                                                                             72.91                                                                              80.66                                 TOTAL     100.00                                                                             100.00                                                                             100.00                                                                             100.00                                                                             100.00                                                                             100.00                                                                             100.00                                __________________________________________________________________________     .sup.1 Offered by Allied Chemical Company as AC 540A having a weight          average molecular weight of 4271 and having 5% ethylene                       .sup.2 Polydimethylsiloxane offered by Dow Corning as DC200                   .sup.3 Carboxyvinyl polymers offered by B. F. Goodrich                        .sup.4 Preservatives offered by Sutton Laboratories                      

The above composition can be made by adding the following components asdescribed:

    ______________________________________                                        Part          Material                                                        ______________________________________                                        I             Water                                                                         Carbopol 934                                                                  Carbopol 941                                                                  Methyl Paraben                                                                Propyl Paraben                                                                Glycerin                                                        II            Sunscreen Agents                                                              Cetyl Alcohol                                                                 Glycerol Stearate                                                             Steareth-100                                                                  Stearic Acid                                                                  Dimethicone                                                                   Petrolatum                                                                    Ethylene/Acrylate Copolymer                                     III           Tetrasodium EDTA                                                              Potassium Hydroxide                                                           Titanium Dioxide                                                IV            Tyrosine                                                                      Imidazolidinyl Urea                                                           Perfume                                                         ______________________________________                                    

The composition is made by mixing the water phase (Part I) materials at71°-99° C. in a scale-mounted mix tank fitted with baffles and anagitator. The oil phase (Part II) is mixed at 71°-110° C. in a separatemix tank fitted with an agitator. Both Part I and Part II are mixeduntil homogeneous phases are obtained.

The water phase (Part I) is then pumped into the oil phase (Part II) inan amount equal to 60-110% of the oil phase (Part II). This oil/waterpremix is held at a temperature of from about 71°-99° C. and agitateduntil a homogeneous mixture is obtained. The oil/water premix is thenpumped into the remaining water phase (Part I) and held at a temperatureof from about 71°-99° C. Part III ingredients are then added whilemaintaining agitation and holding the temperature at 71°-99° C. Thecomposition is then passed through a closed vessel equipped with anultrasonic probe at the flow rate of 0.5-6.5 kg/min. The ultrasonicfrequency may range from 15 to 40 kHz. The composition is furtherprocessed through a heat exchanger and/or jacket cooling to atemperature of 71°-99° C. The part IV components are then added whilemaintaining agitation until a homogeneous mixture is obtained.

The composition is then pumped through a heat exchange to cool to21°-32° C. While waiting to reach steady-state operation, thecomposition may be recirculated back to the mix tank. The composition isthen packed into glass bottles.

The sunscreen composition of Examples 11 is rubbed onto the skin of theperson in need of protection from UVA and UVB wavelength radiation. Athin layer of this sunscreen composition is applied to the skin whichwill be exposed to the radiation. This sunscreen composition easy toapply to skin, and the sunscreen agent is not readily absorbed by theskin or readily rubbed off. Furthermore, it provides a constant and evenprotection against both UVA and UVB radiation.

EXAMPLE 15 Skin Penetration by Sunscreen Agents of the Present Invention

Skin penetration is done with human abdominal skin (Shriner's BurnsInstitute) mounted on a ground-glass diffusion cell. The skin surfacearea exposed is 0.785 cm². The sunscreen agents are applied as asolution (100 microliters) in a vehicle (either ethanol or dimethylisosorbide). The receiving reservoir is 4.5 ml of vehicle. The reservoiris stirred and maintained at 37° C. Penetration is determined by readingthe UV absorbance of the reservoir. Assays are done in triplicate.

Penetration of Sunscreen Agents of the Present Invention vs. CommonlyUsed Sunscreen Agents

    ______________________________________                                                               Total Material                                                                Penetrated in 24 hrs.                                  Sunscreen              (ug/cm.sup.2)                                          ______________________________________                                        2-ethylhexyl 4-N,N-dimethylaminobenzoate                                                             70                                                     (ethanol vehicle)                                                             2-hydroxy-4-methoxybenzophenone                                                                      21                                                     (dimethyl isosorbide vehicle)                                                 Compound 4             no penetration                                         (ethanol vehicle)                                                             ______________________________________                                    

The low amount of skin penetration by the sunscreen agents useful in thepresent invention provides a uniform layer of protection for the skinagainst both UVA and UVB radiation. This protection against the UVA andUVB radiation will not vary with time as might occur by using a mixturecontaining molecules that are absorbed and/or rubbed off at differentrates. Also, the relative UVA to UVB protection will not vary with timefor the sunscreen agents of the present invention. Furthermore, theprotection by the sunscreen agents of the present invention should lastlonger because it is less readily lost by absorption through the skin.Finally, there is less potential for toxicity (typically in the form ofskin irritation) for the sunscreen agents of the present invention dueto this low amount of skin penetration.

What is claimed is:
 1. A sunscreen compound having the structure:

    X--B--Z

wherein (a) --X is a UVA-absorbing moiety selected from the groupconsisting of those having the structures: ##STR14## (b) --Z is aUVB-absorbing moiety having the structure: ##STR15## (c) --B-- is alinking group selected from --O-- and --NR--; wherein, in the abovestructures, --A is selected from the group consisting of --R, --OR,--N(R)₂ or --SO₃ H, or its pharmaceutically-acceptable salt or ester;each --A² is independently --OR or --N(R¹)₂ ; --A³ is --H or --OH; --A⁴and --A⁵ are, independently, --R or --OR, and wherein further either--A³ or --A⁴ must be --OH; --A⁶ is --H or --SO₃ H, or itspharmaceutically-acceptable salt or ester; and each --R and --R¹ isindependently selected from the group consisting of --H, straight orbranched chain alkyl having from about 1 to about 20 carbon atoms,--(CH₂ CH₂ O)_(m) H, or --(CH₂ CH(CH₃)O)_(m) H, wherein m is an integerfrom 1 to about
 8. 2. The sunscreen compound of claim 1 wherein --A² isselected from the group consisting of --OH, --OCH₃ and --OC₂ H₅, and--B-- is selected from the group consisting of --O-- and --NH--.
 3. Thesunscreen compound of claim 1 wherein --A² is --N(R¹)₂, each --R¹ isindependently straight or branched chain alkyl having from about 1 toabout 20 carbon atoms, and --B-- is selected from the group consistingof --O-- and --NH--.
 4. The sunscreen compound of claim 1 wherein --Xhas the structure: ##STR16## wherein --A is --R.
 5. The sunscreencompound of claim 4 wherein --A² is selected from the group consistingof --OH, --OCH₃, --OC₂ H₅ and --N(R¹)₂, each --R¹ is independentlystraight or branched chain alkyl having from about 1 to about 20 carbonatoms, --B-- is --O--, and --A is --H.
 6. The sunscreen compound ofclaim 1 wherein --X has the structure: ##STR17## wherein --A⁵ is --R,and either --A³ or --A⁴ is --H.
 7. The sunscreen compound of claim 6wherein --A² is selected from the group consisting of --OH, --OCH₃,--OC₂ H₅ and --N(R¹)₂, each --R¹ is independently straight or branchedchain alkyl having from about 1 to about 20 carbon atoms, --B-- is--O--, and --A⁵ is --H.
 8. The sunscreen compound according to claim 1wherein --A² is selected from the group consisting of --OCH₃, --OCH₂CH₃, --OH and --N(R¹)₂ ; and each --N(R¹)₂ has one R¹ group beingstraight or branched alkyl having more than 2 carbon atoms and the otherR¹ group is methyl or ethyl; and --B-- is selected from the groupconsisting of --O-- and --NH--.
 9. The sunscreen compound according toclaim 5 or 7 wherein --N(R¹)₂ has one R¹ group being straight orbranched alkyl having more than 2 carbon atoms and the other R¹ group ismethyl or ethyl.
 10. The sunscreen compound according to claim 5 or 7wherein --A² is --OCH₃.
 11. The sunscreen compound according to claim 1selected from the group consisting of 4-methoxycinnamic acid ester with4-hydroxydibenzoylmethane; and 4-methoxycinnamic acid ester with4-hydroxy-4'-methoxydibenzoylmethane.
 12. A sunscreen compositioncomprising:(a) a sunscreen compound of any of claims 1, 4, 5, 6, 7 or 8;and (b) a pharmaceutically-acceptable sunscreen carrier.
 13. A methodfor protecting the skin of humans or lower animals from the effects ofUVA and UVB wavelength radiation, said method comprising topicallyapplying to the skin of the human or lower animal an effective coatingof a sunscreen composition comprising a compound of any of claims 1, 4,5, 6, 7 or 8.